1. Field of the Invention
Embodiments of the present invention relate, in general, to using densified fluid as a primary solvent to process articles and more particularly to systems and methodology for using liquified carbon dioxide to process (clean) textiles across a barrier separating two distinct environments.
2. Relevant Background.
Traditionally the cleaning of textiles involves two basic approaches; a traditional water-based or a dry-cleaning method in which water is replaced by trichlor-ethylene or perchlor-ethylene (PCE, aka PERC). Generally articles of clothing or textiles are placed in a treatment drum of a washing machine in which clean fluids, water based or otherwise, are added. The drum agitates the combination of the cleaning fluids and textile to aid in the breakdown and removal of contaminates. Thereafter the solvent is drained carrying with it containments originally found in the textiles. The process for dry cleaning is essentially the same but for the fact that the solvent used to clean the textiles is not water based but a chemical solution. These dry cleaning solutions are, from an environmental standpoint, not environmentally friendly and are also associated with health and safety risks. PCE for example is a suspected carcinogen and petroleum-based solvents are flammable as well as being linked to ozone depletion.
While there exists numerous cleaning systems and numerous environments in which they operate, the demands of cleanliness associated with a clean room environment are particularly challenging.
A clean room is an environment typically used in manufacturing or scientific research that has a low level of environmental pollutants such as dust, airborne microbes, aerosol particles and chemical vapors. More accurately, a clean room has a controlled level of contamination as specified by the number of particles per cubic meter at a specified particle size. For example, ambient air outside in a typical urban environment contains 35 million particles per cubic meter in the size range of 0.5 μm and larger in diameter. Such an environment corresponds to an ISO 9 clean room while an ISO 1 clean room allows no particles in that size range at all and only 12 particles per cubic meter of 0.3 μm and smaller size range.
One approach to textile cleaning that can meet clean room environment standards is the use of liquid carbon dioxide as the cleaning medium. An exemplary carbon dioxide cleaning system is disclosed in the U.S. Pat. No. 4,012,194. In this patent a simple cleaning process is disclosed in which textiles are placed in a cylindrical vessel to which carbon dioxide is introduced. The liquid carbon dioxide passes through the textiles, removing soil and is thereafter passed to an evaporator. The evaporator vaporizes the carbon dioxide leaving the soil or other contaminants behind. The carbon vapor dioxide is thereafter pumped to a condenser after which the liquid carbon dioxide is produced and thereby returned to a refrigerated storage tank for later use. Other dry cleaning systems using similar technology and processes are widely known. In such technologies a pressure vessel in which liquid carbon dioxide is introduced is generally maintained between 300 to 1000 PSI. Additional additives, such as organic solvents, may be supplemented to the liquid carbon dioxide to enhance the cleaning experience. And once a cleaning cycle has been completed the pressure vessel is depressurized and clean textiles removed. Despite the ability of a system such as the one presented above to effectively clean textiles it faces a fundamental flaw in that the textiles, once cleaned as a result of its process, are immediately introduced into a dirty environment that places the textiles “cleanliness” into question.
Clean rooms can be very large. For example entire manufacturing facilities can be contained within a clean room environment and have factory floors covering thousands of square meters. Such environments are used extensively in semiconductor manufacturing, aerospace, biotechnology, life sciences and other fields that are very sensitive to environmental contamination. Typically the air entering a clean room from the outside is filtered to exclude dust, and the air inside is recirculated through high-efficiency particulate air filters to remove internally generated contaminants. Staff enter and leave through air locks (sometimes including an air shower stage), and wear protective clothing such as hoods, face masks, gloves, boots and coveralls. Equipment inside the clean rooms are designed to generate minimal air contamination and clean room furniture is designed to be easily cleaned. Common materials such as paper, pencils, and fabrics made from natural fibers are often excluded, and alternatives are used. Moreover, clean room environments are often kept at a positive pressure so that if there are any leaks air escapes outward rather than contaminated air being allowed to enter the clean environment. Also, many clean rooms include an anterior room (known as a “grey room”) in which clean room clothing must be put on prior to entry and from which a person can walk directly into the clean room and begin work.
One important consideration in a clean room environments is textiles. It is important to note that because the human body produces so many contaminants in such large quantities, the maintenance and the supply of clean room apparel is critical and such textiles can easily be overwhelmed by contaminants. Accordingly clean room textiles are changed and cleaned frequently and textile cleaning system configurations are often evaluated for the level of cleanliness desired. Indeed the entire construction and maintenance of a clean room environment often includes a textile configuration and clean room plan to address the maintenance and testing of clean room apparel. For example it is conceivable that each worker in a clean room environment must use a new clean room textile upon each entry into the environment. Thus a large manufacturing facility could find the need for hundreds of clean room textiles each day. Over several years the contamination control industry has produced innovative systems and apparel to assist humans working in clean room environments thereby protecting the product and the processes from contamination. However, as alluded to above, these systems (textiles) require care and vigilant attention.
Clearly one critical step in producing a clean room textile is validation of a clean room textile supply and cleaning system. Such evaluation and validation often includes a complete audit of the textile system supplier site and the processes used to supply clean room textiles. While such a supplier may possess the capability of producing clean room textiles at a specified level of cleanliness for a required clean room environment, one has to consider not only the cleaning process but also the environment in which the cleaning takes place as well as packaging and transport. For example the removal of a clean textile from the cleaning apparatus into a non-clean room environment places the certification and validity of the clean textile at risk. Indeed the facilities cleaning and packaging the clean room textiles must be at or better than the same cleanliness standard of the targeted clean room or risk the likely possibility that the mere introduction of supposedly “clean” textiles into a dirty environment is, by itself, introducing unacceptable contaminants.
One limitation of the prior art therefore is that in each case of the prior art the introduction and removal of the textiles occurs through the same environment. That is to say, the clean textiles removed from the cleaning apparatus are introduced into an unclean environment. While for a typical cleaning process such an introduction of clean textiles into a non-clean environment is not significant, for textiles destined for a clean room environment the mere transport of cleaned textiles within a non-clean environment can introduce contaminants that may defeat the entire purpose of having such a extensive cleaning process. Such situations are typical in environments in which contaminants on the order of a few particles per million require the rejection of a textile. Examples include certain semiconductor, electronic and pharmacology locations.
What is needed therefore is an apparatus and associated methodology for cleaning articles using densified gas such as liquid carbon dioxide wherein soiled articles are introduced to the apparatus from a first environment and the clean articles are removed from the device into a separate clean environment. These and other challenges of the prior art are addressed by one or more embodiments of the present invention.
Additional advantages and novel features of this invention shall be set forth in part in the description that follows, and in part will become apparent to those skilled in the art upon examination of the following specification or may be learned by the practice of the invention. The advantages of the invention may be realized and attained by means of the instrumentalities, combinations, compositions, and methods particularly pointed out in the appended claims.